Assessment of the nutritive value of fungi treated maize cob using in vitro gas production technique

A Akinfemi, O A Adu* and F Doherty**

Nasarawa State University, Keffi,Faculty of Agriculture, Department of Animal Science, PMB 135, Shabu-Lafia, Nigeria
akinjournal2000@yahoo.com
Department of Animal Production and Health, Federal University of Technology, Akure, Nigeria
** Department of Biological Science, Yaba College of Technology, Lagos, Nigeria

Abstract

The objective of the current study was to assess the changes in nutritive value of fungal treated maize cobs using in vitro gas production technique. Treatment of crop residues with some species of white-rot fungi can enhance the nutritive value. After the fungal treatment of maize (Zea mays L) cob with two white-rot fungi in a solid state fermentation, the chemical composition and in vitro digestibility of the resultant substrate was determined.

The results show a significant (p<0.05) increase in crude protein (CP) contents from 6.82% for the control (UM) to 10.05% for Pleurotus pulmonarius (PPM) and 10.37% for Pleurotus sajor caju (PSM). The ash and ether extracts (EE) contents also increased significantly (p<0.05). The crude fibre (CF) decreased significantly from 32.68% for UM to 22.89 for PPM and 24.14% for PSM. There were also consistent significant decreases (p<0.05) in the values obtained for cell wall contents (NDF, ADF ADL). Over utilization of the hemicellulose and cellulose by the fungi as energy source decreased the NDF. The estimated organic matter digestibility (OMD) ranged from 38.06 to 42.09%, metabolisable (ME) ranged from5.49 to 6.04 MJ/Kg DM and short chain fatty acid (SCFA) ranged from 0.4339 to 0.4974 µM. There were no significant (p>0.05)  difference in the values obtained for the degradation of the insoluble fractions (b) ML.

Gas production rate constant (c) was faster in the fungal treated maize cob compared with the untreated. This result suggests that fungal treatment of maize cob resulted in improved CP and digestibility, hence its potential in ruminant nutrition.

Key words: chemical composition, crop residues, in vitro digestibility, solid state fermentation, white-rot fungi

Introduction

The major constraint to livestock production in Nigeria is the scarcity of quality and sufficient supply of feed throughout the year. This is more so because of the competition between man and livestock for the available food grains. Addition to this is the increasing population at a very high rate, especially in developing countries like Nigeria. With the increasing demand for livestock products in the world economy and shrinking land area, future hope of feeding the nations and safeguarding their food security will depend on their better utilization of their non-conventional feed resources, which cannot be used as food for human (Makkar 2000).

The use of crop residues in animal feeding is a very common practice in tropical countries. However, these feed resources have generally been directed to ruminant production, due to the high level of the cell wall fraction (Preston and Leng 1987). An important class of non-conventional feedstuff in Nigeria is maize cob which is obtained during the processing of harvested maize. The amount of maize cob generated annually in the country increases as more people venture into the cultivation of maize cobs. In the developing countries, ruminants are feed low quality roughages in various proportions depending on the type of animal and season. But these non-conventional feedstuffs have low feeding value because of its poor protein content, energy, minerals and vitamins.

The quality of crop residue may be improved by physical or chemical methods, but their practical uses are limited by cost and most especially are safety concern that may result from improper handling. Information abounds on physical and chemical treatment but there is paucity of information on biological treatment of feed. Mushrooms have been reported to be capable of transforming nutritionally worthless waste into protein rich food and have been confirmed to be source of single cell protein (Kurtzman 1981; Alofe et al 1998). The cultivation of Pleurotus sajor-caju and Pleurotus pulmonarius on maize cobs may thus be a biotechnological process of converting maize cobs, which are considered to be waste into value added ruminant feed.

This study is therefore conducted to assess the changes in nutritive value of fungal treated maize cobs using in vitro gas production technique.

Materials and methods 

Samples

Dried samples of maize residues (maize cob) and were collected from the Teaching and Research Farm, University of Ibadan, Ibadan, Nigeria. The materials were milled and oven-treated at 65^oC until a constant weight was obtained for any dry matter

The fungus

The sporophores of Pleurotus pulmonarius and Pleurotus sajor caju growing in the wild were collected from Ibadan University botanical garden. These were tissue cultured to obtain fungal mycelia (Jonathan and Fasidi 2001).The pure culture obtained was maintained on plate of potato dextrose agar (PDA).

Degradation of maize cob by Pleurotus pulmonarius and Pleurotus sajor caju

Preparation of substrate

The jam bottles used for this study were thoroughly washed, dried for 10 min. at 100^oC. 25.00g of the dried milled substrate were weighed into each jam bottle and 70ml distilled water were added. The bottle was immediately covered with aluminium foil and sterilized in the autoclave at 121^oC for 15 min. Each treatment was triplicates.

Inoculation

Each bottle was inoculated at the centre of the substrate with 2, 10.00mm mycelia disc and covered immediately. They were kept in the dark cupboard in the laboratory at 30^oC and 100% RH (Relative humidity). After 21 days of inoculation, the experimental bottles were harvested by autoclaving again to terminate the mycelia growth. Samples of the biodegraded samples were oven dried to constant weight for chemical analysis and in vitro digestibility.

In vitro gas production

Rumen fluid was obtained from three West African Dwarf female goat through suction tube before the morning feed. The animals were fed with 40% concentrate feed (40% corn, 10% wheat offal, 10% palm kernel cake, 20% groundnut cake, 5% soybean meal, 10% brewers grain, 1% common salt, 3.75% oyster shell and 0.25% fishmeal) and 60% Guinea grass. Incubation was carried out according to (Menke and Steingass 1998) in 120ml calibrated syringes in three batches at 39^oC. To 200mg sample in the syringe was added 30ml inoculum contained cheese cloth strained rumen liquor and buffer (9.8g  NaHCO₃ + 2.77g Na₂HPO₄ + 0.57g KCL + 0.47g NaCL + 0.12g MgSO₄. 7H₂0 + 0.16g CaCI₂ . 2H₂0 in a ratio (1:4 v/v) under continuous flushing with CO_2.  The gas production was measured at 3, 6, 9, 12, 15, 18, 21 and 24h. After 24 hours of incubation, 4ml of NaOH (10m) was introduced to estimate the amount of methane produced. The average volume of gas produced from the blanks was deducted from the volume of gas produced per sample. The volume of gas production characteristics were estimated using the equation Y = a + b (1 – e^ct) described by Ǿrskov and McDonald 1979, where Y = volume of gas produced at time‘t’, a = intercept (gas produced from the soluble fraction), b = gas production from the insoluble fraction, (a + b) = final gas produced, c = gas production rate constant for the insoluble fraction (b), t = incubation time. Metabolisable energy (ME, MJ/Kg DM) and organic matter digestibility (OMD %) were estimated as established (Menke and Steingass 1998) and short chain fatty acids (SCFA) was calculated as reported Getachew et al (1999).
 

ME = 2.20 + 0.136* GV + 0.057* CP + 0.0029*C;

OMD = 14.88 + 0.88GV + 0.45CP + 0.651XA;

SCFA = 0.0239*Gv – 0.0601
 

Where Gv, CP, CF and XA are net gas production (ml/200mg, DM) crude protein, crude fibre and ash of the incubated sample respectively.

Chemical composition

Dry matter of the samples was determined at 105^oC for 8 hours. Nitrogen (N) content of the milled dried samples was determined by the standard Kjeldhal method (AOAC 1995) and the crude protein (CP) was calculated (N x 6.25).Ash content was determined using muffle furnace. Neutral detergent fibre (NDF), Acid detergent fibre (ADF) and Acid detergent lignin (ADL) was determined using the method described by Van Soest et al 1991.Hemicellulose was estimated as the difference between NDF and ADF, and cellulose estimated as the difference between ADF and ADL

Statistical analysis

Data obtained were subjected to analysis of variance (ANOVA) and mean separation when there were significant differences was by Duncan multiple range test using Statistical Analysis System (SAS) 1998 package.

Result and discussion 

Changes in chemical composition

The result of chemical composition of the treated and untreated maize cob is given in Table 1. 

There were variations in the chemical composition of the treated and untreated maize cobs, with CP ranging from 6.82% to 10.37%, CF from 241.14% to 32.68%, NDF from 62.52 to 68.37%; ADL from 11.48 to 13.79%, ADF from 44.56 to 47.04%, cellulose from 32.24 to 33.08% and hemicellulose from 17.96 to 21.31%. The increase observed in the CP content of the fungal treated maize may probably be due to addition of fungal protein during solubilization and degradation (Belewu and Belewu 2005). CP increase could also be as a result of hydrolysis of starch to glucose and its subsequent use by same organism as a carbon source to synthesise fungal biomass rich in protein (Bender 1970; Hammond and Wood 1985). This agrees with the findings of Zadrazil 1993; Belewu and Okhawere 1998 who reported that the colonization of lignocellulosic waste by the fungi results in increase in their nutritional value. The decrease in the value of detergent fibre (hemicellulose, cellulose and lignin) and acid detergent fibre (lignin and cellulose) for the fungal treated maize cobs could be indicative of the degradation of the cell wall component of the substrates produced by extra cellular enzymes of P.ostreatus. Previous authors concluded that lignifications of structural polysaccharides not only inhibited ruminal microbial digestion of polysaccharide by forming 3-D matrix, but also that the presence of highly lignified tissues formed a physical barrier preventing accessibility of the otherwise highly digestible tissue to the action of hydrolytic enzymes of the rumen micro-organism ( Karunanandaa et al 1995), and have shown that increased digestibility was associated with the degradation of structural carbohydrates (Mukherjee and Nandi  2004).

Estimated organic matter digestibility (OMD), short chain fatty acid (SCFA), metabolisable energy (ME) and methane (CH₄) production

The estimated OMD, ME and methane is shown in Table 2.

The estimated OMD was significantly higher in the fungal treated cobs compared with the untreated. The value of OMD in the present study were higher than those of rice straw, linseed straw, date stone sugar bagasse (Sallam et al 2007), wild cocoyam (Babayemi and Bamikole 2009), spent tea leaf (Babayemi 2006) mixtures of Tephosia candida and guinea grass (Babayemi and Bamikole 2006) the higher estimated OMD obtained in the fungal treated cobs implies that the microbes in the rumen and animal have increased nutrient uptake (Chumpawadee et al 2007).

The predicted ME also differed significantly (p<0.05) with higher value obtained in the treated substrates. These value are comparable to soyabeans hull, broken rice, mung bean, meal and rice bran (Chumpawadee et al 2007) and lower than that estimated for different parts Enterelobium cyclocarpum (Babayemi 2006). Menke and Steingass (1988) reported a strong connection between ME values measured in vivo and predicted from 24h in vitro gas production and chemical composition of feed. The in vitro gas production method has also being widely used to evaluate the energy value of several classes of feed (Getachew et al 1998; Getachew et al 2002; Aiple et al 1996). Krishnamoorthy et al (1995) also suggested in vitro gas production technique should be considered for estimating ME in tropical feedstuffs; because of evaluating ME by other technique require labour, cost and time .

The SCFA predicted from gas production were 0.4339µM, 0.4817µM and 0.4975 µM for the control (UM), PSM and PPM respectively. There were significant differences among the substrate with higher values obtained in the treated substrates. The higher estimated SCFA in the treated substrate might be due to increase in the CP and decrease in CF. The gas production from different classes of feed (Blummel et al 1990) incubated in vitro in buffered rumen fluid was closely related to the production of SCFA which was based on carbohydrate fermentation (Sallam et al 2007). Getachew et al (2002) reported the close association between SCFA and gas production to estimate the SCFA production from gas value, which is an indicator of energy availability to animal.

In vitro gas production characteristics

Fermentation of the insoluble but degradable fraction (b) though numerically higher in the treated substrate but was not significantly different (p>0.05). Although this is contrary to expectation, but from in vitro gas production pattern (Figure 1) more gas production was still possible beyond 24h, and when this happens, a positive increase in (b) mL is envisaged.

The high rate of fungal treated maize cobs could be related to its high CP content and low content of NDF, ADF and ADL (Osuga et al 2006). Kamalak et al (2005) and Abdulrazak et al (2000) reported that gas production and estimated parameters are negatively correlated with NDF and ADF.

Fungal treatment had significant (p<0.05) effect on the methane production. The value obtained was highest in the control (UM) followed by PSM and PPM. Methane production has negative effect on the animals in one hand as it is an energy loss to the animal and on the other hand, when accumulates in the rumen, it results in bloat (Babayemi 2006).

Gas volume

Gas volume over a period of 24h is presented in Table 3.

The final gas produced ranked from the highest to the lowest were PPM, PSM and UM, and differed significantly (p<0.05). Menke et al (1979) suggested that gas volume at 24h after incubation is indirect with metabolisable energy in feedstuffs. Sommart et al (2000) suggested that gas volume is a good parameter from which to predict digestibility, fermentation end- product and microbial protein synthesis of the substrate by rumen microbes in the in vitro system. Furthermore, in vitro dry matter and organic matter digestibility were shown to have high correlation with gas volume (Sommart et al 2000; Nitipot and Sommart 2003). Gas volume has also shown to have a close relationship with feed intake (Blummel and Becker 1997) and growth rate (Blummel and Orskov 1993).

Conclusion  

• The result obtained in the study indicated that treatment of maize cobs with Pleurotus sajor-caju and Pleurotus pulmonarius enhanced the crude protein content of the substrate while crude fibre was reduced.

  
  

• In vitro digestibility of the treated substrate was also improved.

  
  

• Finally, fungal treatment of maize cob would considerably be of beneficial effect to livestock if included in the diet of ruminant. However, more work is required in this area with the use of live animals.

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Received 8 April 2009; Accepted 10 July 2009; Published 1 November 2009

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